After growing at the rate of 1 percent per year in the last decade, daily emissions of heat-trapping carbon dioxide suddenly plunged by as much as 17 percent globally in early April as the world responded to the covid-19 pandemic.
In some countries, the drops were bigger: 30 percent in the United Kingdom, and 32 percent in the United States, as the global response to the spreading coronavirus shut down air travel, emptied streets and slowed the thrum of industrial machinery.
Traffic restrictions accounted for 43 percent of the emissions drop, and reduced power and industrial production also accounted for 43 percent, said scientists with the Global Carbon Project, which conducted the study tracking the day to day changes in emissions, published in Nature Climate Change.
Annual emissions for 2020 will decline by about 4 percent if economic activity and mobility return to normal by mid-June, or by 7 percent if some restrictions remain worldwide until the end of the year, the study projected—in either case, the largest single annual decrease in absolute emissions since the end of World War II.
Lead author Corinne Le Quéré, director of the Tyndall Centre for Climate Change Research, said one of the main motivations for doing the study was a steady stream of questions from journalists about how the shutdowns would affect greenhouse gas emissions.
"I was bombarded by those questions," she said. "I realized, all of a sudden, you don't have the data, you don't have a clue. And then in the process of getting the information, you see that it is super-interesting." She added that for one thing, it shows how behavioral changes affect emissions in real-time, which can show how the effectiveness of potential policy measures like reducing traffic.
"We can say, 17 percent is quick, but it's not a lot in terms of addressing climate change. And the biggest question for me was, where are the rest, the 87 percent of remaining emissions, coming from?" she said. Identifying those sources would be equally useful in shaping future efforts to cut emissions.
She said the main message the study's authors want to convey is, "This is not the way to tackle climate change."
"You need structural change," Le Quéré, said. "If we do nothing, people will go to back to individual cars, maybe more than before because they want to avoid buses or trains, and emissions could be higher than before."
Tiny Effect on Global Temperature
As emissions bottomed out under lockdowns in early April, the planet was heating up to a near-record high for the month, just 0.04 degrees Fahrenheit cooler than April 2016, according to the National Oceanic and Atmospheric Administration's monthly State of the Climate Report.
Other short-term influences like an emerging La Niña or Arctic weather patterns are much bigger factors. Despite the short-term emissions decline, scientists are still projecting that 2020 will be one of the planet's top two or three warmest years on record.
That helps show that short-term emissions decline resulting from the pandemic response is only a blip in the big picture of climate change, said climate ecologist Pep Canadell, director of the Global Carbon Project and co-author of the study.
"We emit 40 billion tons of CO2 every year. This year, we may emit 37-38 million tons, which makes no difference to the climate or much to the remaining carbon budget of the Paris agreement targets," he said.
Emissions will surge again after the pandemic. We don't know exactly when. However, this dynamic is not particularly important," he said. "We should focus on understanding the long-term impact of the crisis. It took a decade for the global economy to completely come out from the economic crisis (of 2008); this one is bigger. If growth is very sluggish for a long time, that could trick us to think we are doing just fine with our climate mitigation."
He continued, "To me, the most interesting thing coming from the data is the large fraction of the drop in emissions due to road transport, which goes to say how much it can help us to curb emissions if we move mobility to a low carbon path. "We are doing quite well greening the electric grid, and there is a huge opportunity to accelerate the electrification of mobility, including cars, bikes, and scooters."
A Vexing Question
Even as the pandemic idled factories and oil tankers, the concentration of carbon dioxide reached a new high at the observatory atop Mauna Loa in Hawaii at 416 parts per million, growing 3 parts per million from last April.
That relentless growth, juxtaposed with the current short-term emissions decline, raises a vexing question: Why is the response to the coronavirus so forceful compared to lackluster efforts to tackle global warming, which will kill even more people in the decades ahead, with heat waves, storms and famines?
"There's an equity dimension. The pandemic hits everyone. With climate change, people have a feeling that it's more distant, that it won't affect them personally," she said.
In the response to the pandemic, most can understand how their own actions affect the safety of others. With global warming, "some people feel like their own climate footprint is small compared to others," she said."Some people have a feeling that, even if I change, people who have much more impact don't change, so my actions aren't meaningful."
Last January, Otto and other researchers published a study on social tipping mechanisms that could shift societal change toward climate stability. They considered including events like a global pandemic as things that could spark social change.
"Wars and pandemics were on the long list, but we decided to focus on social tipping mechanisms that align with sustainable development goals that benefit people," she said. A pandemic that kills tens of thousands doesn't fit that criterion, reinforcing the idea that forcing people to change social behavior is not the way to address climate policy, she added.
"Without profound structural changes or new regulations, there will be a rebound effect," Otto said. At the same time, this may be a window of opportunity. Maybe people will realize how vulnerable we are, that consumption is not as important as your health, or your family," she said.
The carbon dioxide dampening effect of the pandemic response won't massively shift global climate policy all at once, but it does create a window for incremental change, said Joeri Rogelj, a climate scientist at Imperial College London's Grantham Institute and an author of carbon budget sections in recent major reports from the Intergovernmental Panel on Climate Change.
In response to the pandemic, some cities are already eyeing long-term shifts to reduce urban car traffic, and there are debates in some countries about attaching climate-related conditions to some stimulus funding and whether or not to support old fossil fuel infrastructure like drilling and pipelines. Previous global economic shocks, like the oil embargo in the early 1970s, helped spur research and development on energy efficiency and renewable energy.
"We are currently in a position where the economy seems to have come to some sort of standstill," Rogelj said. "The fundamental question is how governments will decide to spend the stimulus that should kick-start the economy again, whether it goes into green investments or whether it means a return to browner, more polluting industries. There is an opportunity for a longer lasting structural change but it remains to be seized."
Stimulus programs, Otto said, should be designed to work toward long-term climate mitigation goals.
"So much money will be pumped back into the economy. Maybe before companies get funding, they should ... be required to submit plans for decreasing emissions, or maybe we give more support to companies that are already moving toward meeting Paris climate agreement goals," she said.
Otto has been studying the sustainability plans of the big fossil fuel companies, which all project a continued increase in production and demand.
"There's a big clash between that and the Paris climate goals. Maybe the shock to the global markets will make them think about the direction of their investments," she said.
The flash crash of global emissions does not constitute even a first step in dealing with the climate crisis. It's an undesirable economic hardship, "a crisis and a trauma from which we can choose to recover in more sustainable and climate-positive ways," Rogelj said.
He added, "The key question becomes which measures governments will now decide upon to recover from this crisis. Will this be driven by short-sightedness? Or will they acknowledge the bigger picture including the need for a deep decarbonisation to tackle the climate crisis?"